1. Field of the Invention
This invention relates to a control apparatus for a light radiation-type rapid heating and processing device for rapidly heating a processed workpiece such as a semiconductor wafer by radiating light including infrared rays to perform processing such as a film formation, dispersion and annealing or the like.
2. Description of the Related Art
In recent years, a high integration and a fine formation of a semiconductor integrated circuit have been required more and more, and a stage for implanting impurities into the Si crystal of a semiconductor wafer through an ion implantation process, for example, has required the formation of a thin dispersed layer of the impurities and the necessity of forming a more shallow junction plane has increased.
In the case of dispersing impurities through an ion implantation process, an implantation stage for accelerating the ionized impurities through an electric field and implanting them into the Si crystal as well as an annealing stage for dispersing the impurities in the crystal while recovering damages applied to the crystal through the implantation process are carried out. A rapid thermal processing (RTP) is necessary for forming a shallow dispersion layer. It is further necessary to rapidly increase the temperature while the surface temperature of the semiconductor wafer is being kept uniform. If the film thickness of the dispersion layer has to be about 0.13 to 0.15 xcexcxcexcm, it becomes necessary to attain a temperature increasing speed of about 150 to 200xc2x0 C./sec.
A light radiation-type rapid heating and processing device for radiating light including infrared rays which radiates light from filament lamps for heating a workpiece such as a semiconductor wafer and the like is preferable for the aforesaid rapid thermal processing (RTP), and it is possible to increase the temperature of the heated substrate up to a temperature of 1000xc2x0 C. or more within several seconds.
FIG. 17 is a view showing a sectional configuration of a light radiation-type rapid heating and processing device (hereinafter abbreviated as a heating and processing device).
A plurality of filament lamps 1 (hereinafter abbreviated as lamps) are arranged in a lamp chamber 2, and a mirror 3 is arranged at the rear surfaces of the lamps 1. A workpiece carrier 5 is installed within a processing chamber 4, and a workpiece to be heated and processed, such as a semiconductor wafer or the like, (hereinafter called a workpiece W) is mounted on the workpiece carrier 5. In addition, the lamp chamber 2 and the processing chamber 4 may be separated by a window 6 such as a crystal window or the like.
FIG. 18 shows a possible configuration of the lamp 1. The lamp 1 is comprised of a circular light emitting tube 1a and a pair of feeding tubes 1b extending in a substantially right angle from end parts of the light emitting tube 1a. A coil-like filament 1c is arranged within the light emitting tube 1a. An end part of the feeding tube 1b is provided with a seal part 1d, and a lead wire 1e is connected to an end portion of the filament 1c through a molybdenum foil 1f as shown in FIG. 18.
In FIG. 17, circular lamps 1 as shown in FIG. 18 are arranged in a concentric manner, for example, and the aforesaid plurality of lamps 1 are lit to cause light including infrared rays radiated from the lamps 1 to be emitted through the crystal window 6 onto the workpiece W installed in the processing chamber. With such an arrangement as above, the workpiece W is rapidly heated and in turn the lamps 1 are turned off to cause the workpiece W to be rapidly cooled.
A control apparatus (not shown) may control the amount of electrical power supplied to each of the lamps 1 in such a manner that the entire workpiece W is uniformly heated, and, for example, the workpiece W is heated to a temperature of 1000xc2x0 C. or more within several seconds.
FIGS. 19 and 20 show an example of the prior art configuration of the control apparatus for controlling the aforesaid lamps. FIG. 19 shows an entire configuration, and FIG. 20 shows a more detailed configuration of the controlling apparatus for controlling each of the lamps.
In FIGS. 19 and 20, reference number 100 denotes a control section constituted by a CPU and the like; 101 is a temperature adjusting device (hereinafter called a temperature adjuster); 102 a thyristor unit; 1 is a lamp and 103 a temperature sensor. As shown in these figures, each of the temperature adjusters 101, thyristor units 102 and temperature sensors 103 is arranged in correspondence with a lamp 1 (or in correspondence with an assembly of lamps). The temperature sensor 103 detects the temperature of the workpiece W to be heated through the light radiated from each of the lamps 1. The temperature detected by the temperature sensor 103 is fed back to the temperature adjuster 101 which feeds the temperature set value (either an analog signal or a digital signal) sent from the control section 100 and the control signal (an analog signal) corresponding to a deviation of the temperature detected by the temperature sensor 103 to the thyristor unit 102.
Each of voltage and current supplied to the lamp 1 is fed back to the thyristor unit 102. The thyristor unit 102 controls the electrical power supplied to the lamp 1 dependent on the aforesaid control signal.
The thyristor unit 102 may have the configuration shown in FIG. 21 where the electrical power supplied to the lamp 1 is controlled by changing the timing during which a gate current flows from SCR2.
As regards the electrical power control by the thyristor, it is possible to apply the following two methods, namely a conductive angle control and a zero-cross control.
In FIG. 21, an alternating current is supplied to the thyristor unit 102 from an AC commercial power supply 21. The thyristor unit 102 is provided with a lamp control circuit 200 comprised of a first thyristor SCR1 and a second thyristor SCR2. When a gate current flows in gates G1, G2 of the thyristors SCR1 and SCR2 of the lamp control circuit 200, the thyristors SCR1 and SCR2 become conductive and a current is outputted from the thyristor unit 102 to the lamp 1 until the current supplied to the thyristors SCR1 and SCR2 becomes 0.
FIG. 22(a) shows an input voltage waveform of the thyristor unit 102. FIG. 22(b) shows an example of the timing of a gate current supplied to gates G1, G2 of the thyristors SCR1, SCR2, wherein 1 indicates a gate current of the first thyristor SCR1, and 2 indicates a gate current of the second thyristor SCR2, respectively. FIG. 22(c) indicates a waveform of an output current when a gate current is provided with the timing illustrated in FIG. 22(a).
The output current from the thyristor unit 102 is a current with an output voltage waveform and an output current waveform as indicated by the hatched sections in FIG. 22(c) being multiplied with each other. When the timing of the gate current applied to each of the thyristors SCR1, SCR2 is changed the output current waveform and the output voltage waveform are changed resulting in that the output power of the thyristor unit, i.e., the lamp input power, are changed.
The control circuit configuration is the same as that shown in FIG. 21. The timing of the gate current of each of SCR1 and SCR2 corresponds to that shown in FIG. 23(b). In this case, 1 indicates the gate current of the first thyristor SCR1 and 2 indicates the gate current of the second thyristor SCR2.
In FIG. 23, the output current and the output voltage when the gate current is supplied with the timing shown in FIG. 23(b) correspond to that shown in FIG. 23(c). That is, as indicated in FIG. 23(c), it is possible to change the lamp input power by outputting a current and voltage with their waveforms being deleted.
However, the aforesaid prior art control system has the following problems.
(1) Problem of Delay in Control
In order to perform a rapid thermal processing (RTP) with the light radiation-type rapid heating and processing device, it is necessary to increase the temperature of the semiconductor wafer more than 1000xc2x0 C. within several seconds while keeping the surface temperature of the semiconductor wafer uniform as described above. In particular, since the thermal radiation characteristic at a peripheral part of the semiconductor wafer is different from that at its central part, it is necessary to increase the temperature rapidly while the amount of heat supplied to the peripheral part is slightly higher than that of the central part so that the temperature of the semiconductor wafer becomes uniform.
Due to this fact, the control apparatus for controlling the lamp power must perform a high speed control over the electrical power supplied to the lamp while the distribution of each of the lamp powers is being properly held.
In the case of using the control systems illustrated in FIGS. 19 and 20, performing such a control as described above exhibited the following problems.
1.) Since the temperature detected by the temperature sensor 103 is fed back to the temperature adjuster 101 for control, a delay may occur due to a delay in sensing caused by the temperature sensor 103, and a high speed control is hard to perform.
2.) Since the response of the thyristor 102 is slow, it is not possible to perform a high speed control over the lamp electrical power. In addition, in the case of performing the aforesaid conductive angle control, it may happen that a noise called a raising noise is generated in the thyristor conduction state. This may lead to performing an erroneous operation of the control system for the device. In addition, since a rush current flows in the lamp filament, the filament may be excessively loaded and may easily be cut.
3.) Although either a digital or analogue control signal can be sent from the controller 100 to the temperature adjuster 101, in the case that a digital signal is sent out, it is necessary to convert it into an analogue signal in the temperature adjuster 101, resulting in a delay during conversion. In addition, in case of sending an analogue signal, it is necessary to convert the digital signal to an analogue signal at the control section 100 resulting in a delay during conversion.
(2) Occurrence of a Higher Harmonic Strain
This problem will be described with reference to the conductive angle control shown in FIG. 22 wherein, as described above, both the output voltage and the output current become as shown in (a) and (b) of FIG. 24 in case an electrical power control is performed at the output side.
In turn, the waveform of the input voltage at the thyristor unit 102 is a voltage waveform of the commercial AC power supply 21 as shown in FIG. 24(c). In addition, the waveform of the input current is the same as that of the output current as shown in FIG. 24(d).
When the input current has a waveform as described above the following problem may occur. The waveform part marked by a circle in FIG. 24(d) is non-linear, which means that a higher harmonic strain may be generated in the input current. Such a higher harmonic strain is undesirable.
A similar problem may also arise in the case of a zero cross control shown in FIG. 23 described above. The part indicated by a circle in FIG. 24(e) denotes a non-linear part where a higher harmonic strain may occur.
(3) Occurrence of Reactive Power
In FIG. 22, when V is the input voltage, I the input current, W is an effective power and a value of Vxc3x97I is the apparent power, the following relation can be assumed when the waveform of the input voltage and the waveform of the input current are sinusoidal waves and have no phase differences:
Vxc3x97I=W
where W can be considered as an output power (a lamp input power).
However, if the strain waveform is applied as shown in FIG. 24(d) a reactive power (=Vxc3x97Ixe2x88x92W) is generated without fail. Accordingly, if one tries to output a certain reactive power W at the strained waveform as shown in (d) of FIG. 24, a higher apparent power of Vxc3x97I as compared with one having a sinusoidal waveform is required.
Similarly, in the case of a zero cross control, the part indicated by an arrow in FIG. 24(e) can be considered as one period, so that a reactive power is generated.
With regard to the aforesaid reactive power, the reactive power is generated once the output power is controlled. This is a substantial problem in the case that an actual device is manufactured.
That is, due to the following reasons, the output power of the thyristor unit 102 is always controlled and the reactive power is generated without fail, so that a power-factor is decreased.
1.) Practically, in the case of the light radiating-type rapid heating and processing device, if a commercial 200 V is supplied to the lamp device, for example, usually a lamp with a rated 180 V, which is lower than the input voltage by about 10%, is used in consideration of a voltage variation of 10%, and a surplus range is applied to the device. Accordingly, even in the case that the lamp is lit using a rated voltage, the output of the lamp device is controlled.
2.) Further, an electrical power supplied to a plurality of lamps is controlled in the case of the light radiation-type heating and processing device although it is possible that their rated voltage is different (the lengths of filaments are different from each other) with respect to the lamps to be used. Also in this case, the output power is always controlled.
In particular, in the case that the light radiation-type rapid heating and processing device is used for the aforesaid rapid thermal processing (RTP), it is necessary that a temperature of the workpiece is rapidly increased up to about 1000xc2x0 C. in several seconds, and the entire amount of electrical power supplied to the lamp 1 is quite high and ranges from about several tens kW to about 200 kW, and also the input current is quite high. Due to this fact, it is necessary to reduce the occurrence of a reactive power to a minimum in order to improve the efficiency, to reduce the input current and to save energy.
The present invention has been invented with regard to the aforesaid circumstances, and it is an object of the present invention to provide a control apparatus for a light radiation-type rapid heating and processing device in which the temperature of a workpiece can be rapidly increased while its surface temperature is being kept uniform, whose power factor is not reduced and a higher harmonic strain is avoided.
The aforesaid problems are overcome by the present invention as follows.
(1) In a control apparatus for a light radiation-type rapid heating and processing device having a plurality of filament lamps for emitting light including infrared rays onto a processed substrate to cause the processed substrate to be rapidly heated, the region where the plurality of filament lamps are arranged is divided into a plurality of zones corresponding to a distance from the center of the region and at least one filament lamp is installed in each of the zones. The aforesaid control apparatus is constituted by a plurality of lamp power control units having switching elements arranged in correspondence with the zones for switching either a sinusoidal alternating current (AC) supplied from an AC power supply or a full-wave rectified sinusoidal alternating current (AC), and a control section. The control section changes the duty factors of ON/OFF signals of each of the switching elements of said plurality of lamp power control units and controls the electrical power supplied to each filament lamp belonging to each of the zones.
(2) In the aforesaid item (1), a time-based changing pattern of the duty factors of the ON/OFF signals of the switching element belonging to each of the zones is calculated with reference to a thermal radiation characteristic of the processed substrate and a mutual interference between the filament lamps belonging to each of the zones, the time-based changing pattern is stored in advance in the control section, the control section reads out the time-based changing pattern and controls the electrical power supplied to each of the filament lamps belonging to each of the zones.
(3) In the above items (1) and (2), there is provided a phase sensing means for sensing the phase of an AC power supply, and the control section changes the duty factors of the ON/OFF signals of the switching elements in each of the zones at a zero cross point of the AC power supply detected by the phase sensing means.
(4) In the above items (1) and (2), there is provided a phase sensing means for sensing the phase of the AC power supply so as to switch the AC sinusoidal current supplied from the AC power supply synchronously with the phase signal of the AC power supply detected by the phase sensing means.
In case of the above item (1), the temperature of the processed substrate can be controlled without delay during control. In addition, the duty factors of the ON/OFF signals of each of the switching elements of the power control unit is changed and each of the electrical powers supplied to the filament lamps belonging to each of the zones is controlled so that the higher harmonics can be reduced and the power factor can be improved resulting in an improved efficiency of the device.
In the invention described in the above item (2), a high speed control can be carried out and the temperature of the processed substrate can be made uniform.
In the inventions described in the above items (3) and (4), it is possible to further reduce the higher harmonics, to improve the power factor and also to improve the efficiency.
As described above, the present invention may provide the following effects.
(1) The control device, in which the region having a plurality of filament lamps arranged therein is divided into a plurality of zones corresponding to a distance from the center of the region with at least one filament lamp being installed in each of the zones, and in which the electrical power supplied to the filament lamps is controlled, comprises a plurality of lamp power control units each of which is arranged in correspondence with a respective zone and has a switching element for switching either the sinusoidal alternating current supplied from the AC power supply or the full-wave rectified sinusoidal alternating current; and further comprises a control part for changing the duty factors of ON/OFF signals of each of the switching elements of each of the plurality of lamp power control units and for controlling the power supplied to each of the filament lamps belonging to each of the zones, resulting in that the temperature of the processed substrate can be controlled without any delay in control. In addition, it is possible to reduce the higher harmonics, improve the power factor and also improve efficiency.
(2) In view of the thermal radiation characteristic of the processed substrate and the mutual interference of the filament lamps belonging to each of the zones, a time-based changing pattern of the duty factors of the ON/OFF signal of the switching elements in each of the zones is calculated, the time-based changing pattern is read out by the control part, and the power supplied to each of the filament lamps belonging to each of the zones is controlled so that a high speed control can be carried out and, at the same time, the temperature of the processed substrate can be made uniform.
(3) There is provided a phase sensing means for sensing the phase of the AC power supply, wherein the control part changes the duty factors of the ON/OFF signal of the switching element in each of the zones at the zero cross point of the AC power supply detected by the phase sensing means, resulting in that the higher harmonics can be reduced further and the power factor can be improved.
(4) There is provided a phase sensing means for sensing the phase of the AC power supply, wherein the lamp power control unit performs a switching of the sinusoidal alternating current supplied from the AC power supply synchronously with the phase signal of the AC power supply detected by the phase sensing means so that the higher harmonics waveform can be reduced, the power factor can be improved and the input current can be reduced.